Reproductive tract pathology caused by Chlamydia infections is the result of the immune responses to the presence of Chlamydia within the female reproductive tract. Both innate and adaptive immune responses are induced as part of the host defense against infection, and specific cytokines and chemokines play a role in regulating these defense mechanisms. Because our previously published data show that TLR3 deficiency leads to a significant decrease in the synthesis of IFN-? during C. muridarum (Cm) infection in OE cells and mice, we hypothesized that IFN-? was likely not a contributing factor to the increased amount of genital tract pathology seen in the TLR3-deficient mice. We further hypothesized that IFN-? was instead a necessary component of the protective immune response to Cm infection. To test these hypotheses, we infected both wild-type and IFN-? KO mice intravaginally with 105 IFU Cm and our preliminary show that IFN-? KO mice had higher chlamydial loads and suffered more genital tract pathology during Cm infection when compared to WT mice. Our data challenge the paradigm that type-1 IFNs are detrimental in the host response to Chlamydia infection that was established by other investigators using interferon ?/? receptor (IFNAR) KO mice. However, one of the exciting outcomes of our in vitro investigations into the mechanisms of the Chlamydia-TLR3 interaction was that TLR3-deficiency leads to an overexpression of several IFN? subtypes. This unexpected finding reveals that TLR3 differentially regulates IFN? and IFN-?, whereby it stimulates the induction of IFN-? during Cm infection in OE cells, while simultaneously down-regulating the expression of IFN?. The over-expression of IFN? during TLR3 deficiency implicates IFN? (and not IFN-?) as a possible contributor to the increased genital tract pathology seen in TLR3-deficient mice and would support the narrative of a type- 1 IFN exacerbating the Chlamydia-caused genital tract pathology reported by others using IFNAR KO mice. The research plan for Specific Aim #1 describes using CRISPR-Cas9 to generate an inbred knock-out mouse strain that is deficient in the gene expression and protein function of IFN? subtypes 2, 4, 12, and 13. Because these four subtypes of IFN? represent the only IFN? subtypes induced during Cm infection of murine genital tract epithelium, this quadruple KO mouse will be an important reagent for us to test the hypothesis that IFN? contributes to reproductive tract pathology during Cm infection both in vitro and in vivo.